1. Field of the Invention
The invention relates to environmentally safe, non-mercury electronic switches. More particularly, the invention pertains to electronic tilt switches utilizing a spherical weight and an environmentally safe electrically conductive, non-mercury fluid having similar performance to mercury switches.
2. Description of the Related Art
The present invention relates to electronic devices that are alternately electrically turned "on" and "off" based on the position of a housing containing a conductive fluid and a spherical weight. This type of device is generally known in the art as a "tilt switch". A typical tilt switch comprises a hollow, enclosed housing or capsule having electrodes within the housing and extending through and outside the housing. Conventionally, a conductive material either in the form of a fluid, a weight or both is placed within the hollow housing. When using a fluid conductor, the housing is aligned in an "on" position when the conductive fluid electrically connects each of the electrodes, allowing the flow of electricity. The housing is aligned in an "off" position when the conductive fluid in the housing does not electrically connect the electrodes, preventing the flow of electricity.
Traditionally, liquid mercury has been the preferred conductive material because it remains fluid at a wide range of temperatures, including room temperature. Also, mercury has been desirable because it has high surface tension, does not wet many surfaces that it contacts, and generally does not become damaged by contact with the electrodes. However, mercury, its vapor and its oxidized products are extremely toxic. Exposure to mercury has been known to cause disorders such as psychiatric problems in humans and disruption the endocrine systems of humans and animals. This has created a need in the art for a non-toxic alternative.
Commonly employed alternatives to toxic mercury switches have been to replace the toxic mercury such as with conductive spheres or environmentally safe fluids. For example, U.S. Pat. No. 5,136,127 teaches a tilt switch having at least one free moving conductive sphere positioned in a housing that moves to an operating position when the weight is biased by gravity by inclination of the housing. However, conductive metal spheres have certain disadvantages. For example, conductive spheres are especially vulnerable to surface damage caused by electrical arcing which commonly occurs when electrical current is made or broken by the spherical conductor moving into contact or out of contact with electrodes. This arcing can create pitting on the surface of the sphere that may corrode the sphere and interfere with the smooth rolling of the sphere during later cycles of its operation.
U.S. Pat. No. 5,751,074 provides a switch having a conductive fluid filing a first portion of a housing and a non-conductive medium filling a second portion of the housing and where gravity or inertial force causes the conductive fluid to move within the housing and electrically connect and disconnect at least two electrodes. However, conventionally used conductive fluids have certain disadvantages. For example, substitute fluids generally do not shift the weight of the housing as mercury does. This frequently causes a liquid switch to rapidly vacillate between the "on" and "off" positions within the housing, causing the electrodes to "sizzle". Also, substitute conductive fluids typically have vastly different densities and viscosities than mercury. This creates problems if conductive fluids do not flow in a housing as a single mass as mercury does. Rather, thin liquids slosh around in the housing or thick liquids slowly ooze within the housing.
The present invention offers a solution to the disadvantages of the related art. The present invention provides a tiltable electrical device comprising a closed housing having at least two electrodes extending from inside, through and outside the housing, an electrically conductive fluid within the housing, said fluid being moveable within the housing in response to a change in attitude of the housing, between a first position wherein said fluid is in electrical contact with at least two electrodes, and a second position wherein said fluid is not in electrical contact with at least two electrodes, and at least one spherical weight inside the housing, said weight being moveable within the housing in response to a change in attitude of the housing, between said first position and said second position. This device is an efficient and non-toxic replacement for conventional mercury switches. Further, the invention provides a process that requires no complex manufacturing steps and is a less expensive alternative than switches of the prior art. The weighted ball functions to transfer the balance of the weight of the housing, causing the conductive fluid to move between the first and second positions and thereby cause the fluid to alternately electrically contact or disengage from the electrodes.